The over-all goal of the proposed research is to investigate the neural mechanisms in the spinal cord that underlie the generation of locomotor output in vertebrates. The studies are being done on the in vitro lamprey spinal cord preparation that generates "fictive locomotion", the pattern of activity recorded from spinal ventral roots known to correlate with the locomotor behavior. I have chosen this primitive vertebrate for study because it has a central nervous system homologous to the CNS of higher vertebrates but has relatively fewer neurons and a relatively simple locomotor behavior. In particular, the goals are to elucidate the cellular and network mechanisms whereby a small portion of the lamprey spinal cord can generate rhythmic activity and to investigate the ascending and descending coupling mechanisms responsible for intersegmental coordination during locomotion. We have recently developed a theoretical framework for studying intersegmental coordination and discovered general properties of intersegmental coupling that can give rise to the appropriate locomotor pattern. Future progress depends on limiting the number of possible ways that the segmental oscillators might be connected. The first objective of the study is a series of experiments designed to identify and investigate the properties of the neurons of the intersegmental coordinating system using a combined anatomical and physiological approach. The second objective is to characterized the internal structure of the spinal oscillators; to establish, in more detail than is currently available, the characteristics of the neurons that generate the rhythmic activity within the spinal cord and the contribution each makes to the generation of rhythmicity. The results of this work will provide new insights into how the neuronal components of the spinal cord are organized to produce the appropriate locomotor behavior and, more generally, insights into how interactions between oscillating networks of neurons are governed.